feat: make LLM timeout configurable (default 5min)

New flag: --llm-timeout / LLM_TIMEOUT (seconds, default 300)
New builder: llmClient.WithTimeout(duration)
Composite action: new timeout input

Keeps 5 minutes as the sensible default but allows tuning for
larger repos or slower models.

llm/client.go

@@ -32,6 +32,12 @@ func NewClient(baseURL, apiKey, model string) *Client {
 }
 
 // WithTemperature sets the temperature for LLM requests (0 = omit, uses server default).
+// WithTimeout sets the HTTP request timeout for LLM calls (default 5 minutes).
+func (c *Client) WithTimeout(d time.Duration) *Client {
+	c.http.Timeout = d
+	return c
+}
+
 func (c *Client) WithTemperature(t float64) *Client {
 	c.temperature = t
 	return c